1. Field of the Invention
THE PRESENT INVENTION relates to a vehicle impact sensor arrangement, and more particularly relates to a vehicle impact sensor arrangement adapted to sense an impact on a side of a vehicle and to activate a safety device within the vehicle such as an air-bag or a seat belt pretensioner.
2. Description of the Related Art
When a vehicle, such as a motor car, is involved in an accident the vehicle can accelerate or decelerate rapidly. In such a situation a person travelling within the vehicle may continue to move at the original speed of the vehicle, due to inertia, and may thus impact with part of the vehicle which has accelerated or decelerated. For example, if a vehicle is subjected to a front impact, the main body of the vehicle may stop relatively rapidly, whilst the person in the vehicle continues to travel forwardly. Thus, in effect, the person travelling in the vehicle is thrown forwardly on to a fixed part of the vehicle, such as the steering wheel or the dash-board. In a side impact situation, however, a person sitting near the site of the impact may be hit by the intruding outer shell of the vehicle before the speed of the main body of the vehicle is changed and very soon after the impact is initiated. These side impact conditions demand special sensor arrangements.
If a safety device is to be activated in response to a side impact, then the sensor which senses the side impact must be able to respond to a side impact in sufficient time to enable the safety device to be deployed before the inside part of the door of the vehicle hits the seat or hits the person sitting on the seat. Because the total distance between the outer skin of the vehicle and the seat is very short, the sensor has to react very rapidly.
It has been proposed previously to mount side impact sensors in the door of a vehicle, even if the safety device is not located in the door. In this case however there is a disadvantage to have to transmit the signal from the sensor on the door to a safety device mounted on the monocoque shell of the vehicle, because the transmission line can be damaged.
U.S. Pat. No. 5,072,966 of Nishitake discloses embodiments of a side impact sensor. The Specification teaches the provision of a shock sensor, in the form of a known acceleration sensitive sensor which is fixed to substantially the central portion in the back-and-forth direction of a vertical wall portion of a side cill of the motor vehicle. Thus the shock sensor is not located on the exterior of the cill, but is located in the interior of the cill. The shock sensors are said to be activated after an elapse of about 5 ms from a side collision in a motor vehicle provided with the described system. The reason for the delay is that the door cill itself must be deformed, before a shock is sensed by the shock sensor.
Since, in a side impact, it is possible for the driver or occupant of a vehicle to be substantially injured approximately 15 milliseconds after commencement of the side impact, a delay of 5 ms before activation of the sensor is not satisfactory.